The present invention relates to power control systems and, in particular, relates to switchgear systems employed to control the coupling of one or more power sources to a load and to one another.
Switchgear systems are widely used by customers of utilities to determine whether and when power is provided to the customers"" loads from the utilities or power grid, or from other power source(s) that are under the control of the customers. Depending upon the situation, customers may desire that all of their power is provided from the utilities, that all of their power is provided from their own power sources(s), or that power is jointly provided from both types of power sources. When power is jointly provided from both types of sources, the switchgear systems also are capable of determining the relative amounts of power provided from each of the two types of power sources. Further, switchgear systems allow customers to supply power that is produced by their own power sources back to the utilities or power grid, for which the customers are paid.
A switchgear system typically determines whether power is provided from the utility to the customer load, or from a customer power source to the load or back to the utility, by controlling the opening and closing of circuit breakers to establish or break connections between the utility, load, and customers power source. In a conventional two-breaker switchgear system, an outside power line carrying power from a utility is coupled to a customer load by way of a first circuit breaker, and the customer load is further coupled by way of a second circuit breaker to the customer power source, which is often a generator set (xe2x80x9cgensetxe2x80x9d). When both the first and second circuit breakers are closed, power can be supplied to the load from both the utility and the customer power source, or from the customer power source back to the utility. When only the first or second circuit breaker is closed, all power being supplied to the load comes from the utility or customer power source, respectively.
Not all switchgear systems allow the direct coupling of a customer power source to the utility power grid. Indeed, early switchgear systems avoided the simultaneous coupling of the two sources to one another. When it was desired to switch from supplying utility power to the load to supplying customer power to the load, or vice-versa, this transfer was accomplished by first decoupling the power source that was originally supplying power to the customer load prior to coupling the other power source to the load. This basic mode of transfer of the load(the xe2x80x9copen transition transferxe2x80x9d), however, is typically undesirable insofar as there is at least a short period of time in which no power source is providing power to the load. Further, switchgear systems that are only configured to perform open transition transfers do not have the capability of coupling the customer power source to the power grid for the purpose of providing power to the power grid.
Thus, modern switchgear systems typically have the capability of coupling a customer power source directly to the utility power grid. In the case where such a switchgear system is switching between providing all power to the load from the utility and providing all power from a customer power source, or vice-versa, there is a period of time in which both the utility and the customer power source are coupled to one another and coupled to the load. This is desirable insofar as it allows for seamless transitioning between power sources from the perspective of the load. Where the period of time during which both sources are coupled to one another is relatively short, this mode of transfer is called a xe2x80x9cclosed transition transferxe2x80x9d; where the period of time is longer, and the relative contributions of power from the two power sources are respectively increased and decreased slowly with respect to one another during that period of time, this mode of transfer is called a xe2x80x9csoft load transferxe2x80x9d or xe2x80x9cload-ramping transfer.xe2x80x9d
However, in order to provide for closed transition or soft load transfers, the complexity of the design of a switchgear system becomes greatly increased. In addition to controlling the timing of the opening and closing of the circuit breakers, the switchgear system must additionally control the operation of the customer power source so that the power output of that power source becomes synchronized with the power of the utility power grid. That is, before the switchgear system can close both of the circuit breakers so that the customer power source is coupled directly to the power grid, the switch gear system must determine that the customer power source is providing power of the same amplitude, frequency and phase of the power provided by the power grid.
In addition to the complexity associated with performing closed transition or soft load transfers, modern switchgear systems are further complicated because the switchgear systems are often designed to perform switching transfers (or to otherwise change the switching status of the circuit breakers) only under certain specified conditions. For example, a standard switchgear system is often designed to usually maintain the connection between the utility and the customer load in a normal mode of operation, and to only break this connection when there is an emergency condition rendering the utility power unavailable, in response to which the switchgear system transfers the load to the customer power source in an emergency standby mode of operation. Another type of switchgear system is designed to leave the normal mode of operation and enter an interruptible rate (or curtailable power) mode of operation whenever the amount of power from the utility exceeds a certain level (or some related quantity such as price exceeds a certain level), or whenever the utility provides a command to do so.
An additional type of switchgear system is designed to operate so that the utility supplies all power required by the load in a normal mode of operation until the amount of power (or total power cost) exceeds a certain level, at which time the switchgear system enters a peak shaving mode of operation and causes the customer power source to become also coupled to the load. The customer power source then supplies any additional power that is needed above the level. A further type of switchgear system is designed to allow a customer power source to supply power back to the power grid, in an export-to-utility mode of operation. Moreover, some switchgear systems are designed to perform certain transfers or other switching operations only in response to commands or information from outside sources such as the utility. Designing a switchgear system to operate in any one of these modes of operation, or in response to different commands or other information, further increases the complexity of the switchgear system.
Although conventional switchgear systems do exist for performing each of the above-described types of functions, such conventional switchgear systems are typically hardwired and custom-designed for use with specific respective customer power sources, loads and applications, and each such switchgear system is typically restricted to performing a particular respective type of transfer or other switching operation, and to operating in a particular respective mode. That is, conventional switchgear systems, due to their being hardwired and custom-designed, are inflexible in terms of the degree to which their operation can be varied to more appropriately fit changing operational circumstances.
It would therefore be advantageous if a switchgear system was developed in which the operation of the switchgear system could be varied to suit changing operational circumstances. It would further be advantageous if such a switchgear system was, in particular, sufficiently flexible to operate in a variety of modes and to perform a variety of different types of transfers, and other switching operations and to operate both in response to and independently of commands or information from outside sources. It would additionally be advantageous if the switchgear system could be caused to vary in its operation only under limited circumstances, in order to reduce the chance that an operator would inadvertently cause the switchgear system to operate in an unintended and inappropriate manner.
The present inventors have discovered that it is possible to design a flexible, configurable switchgear system that can operate in a variety of modes, perform a variety of different types of transfers and other switching operations, and operate both in response to and independently of commands or information from outside sources. To allow for maximum flexibility, the switchgear system is at least partly implemented using software that includes the necessary programming and related information for allowing the switchgear system to operate in such a variety of modes and manners. To guarantee that the switchgear system operates in the proper mode and performs the proper transfers or other switching operations for a given operational situation, the configurable switchgear system further includes an operator interface by which the operator must provide specific information to access and enable the proper mode and switching operations. In the preferred embodiment of the invention, the operator interface includes a port at which a plug-in card or cartridge storing the necessary information can be inserted.
More particularly, the present invention relates to a switchgear system. The switchgear system includes a first switch capable of electrically coupling a first power source and a load, and a second switch capable of electrically coupling a second power source and the load. The switchgear system further includes a control unit coupled to both the first and second switches. The control unit includes a memory that stores software, and the control unit is capable of operating in at least two modes and controlling opening and closing of the first and second switches in accordance with those modes based upon the software. The switchgear system additionally includes an operator interface coupled to the control unit. The operator interface is capable of receiving additional information that enables the operation of the control unit in at least one of the at least two modes.
The present invention further relates to a control system for controlling the switching status of a switch in a switchgear system. The control system includes a first means for storing primary information concerning a plurality of modes of operation regarding the controlling of the switching status. The control system additionally includes a second means for providing a signal to control the switching status in accordance with one of the plurality of modes. The second means provides the signal based upon a subset of the primary information corresponding to the one mode. The control system further includes a third means capable of receiving secondary information from an outside source. The secondary information determines which subset of the primary information is the basis for the signal.
The present invention further relates to a method of controlling a switching status of two switches in a switchgear system. The method includes providing a controller with an interface, and an internal memory in which is stored primary software concerning a plurality of operational modes regarding the controlling of the switching status of the two switches. The method additionally includes coupling a first memory device including secondary software to the interface of the controller. The secondary software causes an activation of a first subset of the primary software concerning a first of the operational modes. The method further includes generating a first control signal to change the switching status of at least one of the switches in accordance with the first subset of the primary software. The method additionally includes replacing, at the interface, the first memory device with a second memory device including tertiary software. The tertiary software causes an activation of a second subset of the primary software concerning a second of the operational modes. The method further includes generating a second control signal to change the switching status of at least one of the switches in accordance with the second subset of the primary software.